There are a number of known object detection devices for electronically alerting visually-impaired persons of obstacles within their environs. (These object detection devices are also called "obstacle" detection devices.) U.S. Pat. No. 3,172,075 to Kay discloses an apparatus for providing information relative to position of objects. The Kay apparatus uses a centrally located transmitter and two laterally displaced receiving elements having directional receptivities which extend into the field of view to detect objects offset from the reference axis of the receiving elements.
U.S. Pat. No. 4,280,204 to Elchinger describes a mobility cane for the blind having a dual-mode ultrasonic obstacle detection apparatus mounted thereon. The ultrasonic detection apparatus produces an audible warning of objects within a predetermined spatial zone having a maximum and minimum zone depth.
U.S. Pat. No. 4,551,825 to Biber discloses an object detection system which periodically changes a sonic energy transmission frequency to periodically change the beam width of a transmission pattern for object direction distinguishing purposes. Variable and fixed pitch audio signals are generated, with the generation and pitch of the variable-pitch signal being object distance dependent, and the generation of the fixed-pitch signal being dependent upon the object presence only.
U.S. Pat. No. 4,680,740 to Treptow discloses an audio aid for the blind which generates a high audio frequency signal modulated by a low audio frequency signal, and emits a directional beam of acoustic energy based thereupon. The acoustic energy reflects off of an object in the vicinity of a user to return a sound signal which can be audibly discerned by the user to detect the presence of the object and its approximate location.
U.S. Pat. No. 4,712,003 to Ban et al. discloses a guide device in the form of a walking stick having a source for emitting infrared radiation and a photoelectric element for receiving the infrared radiation reflected from an object. An electric circuit produces information related to the distance of the object based on the illuminance or energy of received radiation on the photoelectric element. A vibration, which is to be sensed by a user, is then produced having a frequency and amplitude which are dependent upon the distance information produced by the electric circuit.
U.S. Pat. No. 4,761,770 to Kim et al. describes an ultrasonic sensory aid for a blind person which receives a reflected ultrasonic echo signal from an object, stretches the reflected signal in a time axis, and converts the stretched signal into an audible frequency signal.
The prior art devices are not amenable to simultaneously detecting multiple objects or obstacles, nor to conveying information related to the multiple objects to the user in a manner which creates a veridical stereo image of the object and its location.